1. Field of the Invention
This invention relates to an ultrafine Al particle consisting of a multiply twinned particle and a production method thereof.
2. Description of the Related Art
With a diameter of 100 nm or less (ultrafine particles), metal particles have different properties from normal particles (with a diameter of 1 .mu.m or more, for example). New properties may be observed because the number of atoms existing on a particle surface increases relative to total number of atoms of the particle, and an effect of surface free energy cannot be ignored in consideration of the properties of particles.
Ultrafine particles as described above have different properties from bulk materials. They have a lower melting point and a lower sintering temperature than bulk materials, for example. Further, when there are a plurality of ultrafine particles, the tunnel effect or quantum mechanical effects (such as quantum well and mini-band) may be generated among them. Depending on the type of the particles, a high catalyst property may be generated. The ultrafine particles are suitable for finding new surface phenomena and grasping outlines thereof. These properties can be applied to various areas including material properties improvement, development of various devices and application to functional materials including catalysts. Thus, the physical properties and applications of ultrafine particles are studied.
Conventionally, ultrafine particles are produced by physical or chemical methods as described below: Physical production methods of ultrafine particles include an evaporation method in gases, a metal evaporation synthesis method, a vacuum evaporation method on a fluid oil. According to the evaporation method in gases, a metal or the like is evaporated in inert gas, so that ultrafine particles are produced to be cooled and condensed by collision with the gas. As a material for ultrafine particles, metal atoms evaporated by sputtering is also utilized. According to the metal evaporation synthesis method, a metal is heated in a vacuum and the vaporized metal atoms are deposited, together with an organic solvent, on a substrate cooled under a freezing point of the organic solvent. According to the vacuum evaporation method on a fluid oil, a metal is deposited on an oil for production of ultrafine articles.
As chemical methods to produce ultrafine particles, those utilizing a liquid or vapor phase are known. The methods utilizing the liquid phase include a colloid method, an alkoxide method and a coprecipitation method. In the colloid method, a noble metal salt is reduced in alcohol coexisted with a high molecular surface active agent under reflux. In the alkoxide method, it is utilized hydrolysis of a metal alkoxide. In the coprecipitation method, a precipitant is added to a metal salt mixture to obtain precipitated particles.
Ultrafine particle production methods utilizing the vapor phase include an organic metal compound pyrolysis method, a metal chloride reducting/oxidizing/nitriding method, a reduction method in hydrogen, and a solvent evaporation method. In the organic metal compound pyrolysis method, a metal carbonyl compound is pyrolyzed to obtain metal ultrafine particles. In the metal chloride reducting/oxidizing/nitriding method, a metal chloride is reduced/oxidized or nitrided in an air current of reacting gases. In the reduction method in hydrogen, an oxide or a hydrate is heated in a hydrogen current for reduction. In the solvent evaporation method, a metal salt solution is atomized through a nozzle to dry in hot air.
Conventional studies and developments of the ultrafine particles are mainly with regard to an aggregate of various ultrafine particles. Properties and applications of an ultrafine particle as an unit substance are less studied. This fact is also resulted from the above-mentioned production methods of the ultrafine particles. By the conventional production methods, it is difficult to obtain an ultrafine particle as an unit substance.
For example, application of ultrafine Al particles to various functional materials such as catalysts and devices is studied. For such application development, it is preferable to improve the controllability of the crystal direction and crystal plane for controlling the properties of ultrafine Al particle. By conventional production methods, however, it is difficult just to obtain an ultrafine particle as an unit substance. Further, even if the particle as an unit substance are obtained, it is quite difficult to control their crystal direction and crystal plane. This problem obstructs application development of the ultrafine Al particle.